What are some literary elements used in Grunt?

Grunt is a book by author Mary Roach. The full title is Grunt: The Curious Science of Humans at War. Although this book is non-fiction, Roach does use elements often found in narrative, particularly the element of humor.
Humor as a writing device intends to make the audience laugh and can often be used, when used effectively, to bring lightheartedness to difficult or controversial topics, allowing the writer to explore these topics in a unique way.
One important aspect of Roach's humor is the sheer absurdity of some of the content. This element as been explored in Roach's previous works and focuses on the strangeness in which humans often think of solutions to solve a problem. Michelle Dean provides interesting commentary in her review for The Guardian on one particular amusing section in Grunt in which the author details firing chickens at planes.

She starts with an account of the chicken gun, a cannon with a 60ft barrel that fires literal chickens at fighter planes to test the potential that they will be damaged by errant birds during a flight. Of course, as Roach points out, chickens aren’t fliers. The bird’s impact, Roach tells you, is less like that of a duck or goose and more 'like a flung grocery item'.
https://www.theguardian.com/books/2016/jun/13/grunt-mary-roach-review-military-science